This invention relates to improved heating or cooling enclosures or reaction vessels having transparent protrusions, and more particularly, to means and method for reducing the thermal radiation being carried along such protrusions.
Glass, quartz, fused alumina and other optically and thermally transparent materials are widely used as enclosures for heating or cooling of materials. A vitreous quartz diffusion tube or bell jar for the processing of semiconductor materials is a typical example. In this example, the semiconductor materials are heated within a quartz tube in a furnace, epitaxial reactor, or other deposition apparatus. A portion of the quartz tube usually extends outside of the hot zone and is typically terminated by a removable coupling or flange which permits access or observation. Rubber, Teflon, Viton, other elastomers and other thermally sensitive materials are frequently used as gaskets on these flanges. If excess thermal energy is transmitted to these materials from the hot zone of the furnace or reactor they are damaged and stick to the flanges and tubes. It then becomes extremely difficult to separate the flanges from the tube ends without damaging the tubes or flanges or both. This has been found to occur even though the flanges and the extensions of the quartz tube beyond the hot zone are cooled by conductive or convective means. While placing a radiation reflector in the interior of the quartz tube between the hot zone and the flange reduces the amount of radiant heat coupled directly to the flange, it has not served to eliminate the problem of damage to the gaskets.
It has been discovered that a significant amount of radiant energy is coupled to the gasket or attachment areas by means of thermal and optical radiation being carried inside the wall regions of the quartz tubes. The wall regions of the quartz tube act as a "light pipe" carrying thermal radiation from the hot zone to the gaskets or attachment areas of the closure means. High intensity thermal radiation can be carried by the quartz material even though the local temperature of the quartz itself is relatively low. By this means, a large amount of energy can be coupled from the hot zone to the material of the gaskets or attachment areas, independent of the convective or conductive cooling means being applied to the quartz tube or the end flange.
This "light pipe" effect can be easily demonstrated by placing a quartz tube or rod in a high temperature flame. The portion of the rod a short distance outside the flame is cool to the touch, but if one's hand is placed facing the end, the heat being transmitted (carried) along the rod can be readily felt. Thermal radiation burns can result. For the purposes of this disclosure a thermal radiation carrying member, media, or enclosure is one which exhibits this light pipe effect, that is, channeling or carrying thermal radiation by radiant propagation from a hot zone to other regions.
Thus, a need continues to exist for reducing the coupling of radiant energy from hot zones to exterior couplings or flanges of transparent reactor enclosures, this radiation being carried in the walls of the enclosure itself.
Accordingly, it is an object of this invention to provide an improved apparatus for protecting closure means of a radiation carrying member coupled to a hot zone, from the radiant thermal energy being carried by said member between said hot zone and said closure means.
It is a further object of this invention to provide an improved apparatus for protecting a closure flange of a high temperature semiconductor reaction chamber from radiation being piped in the walls of the chamber.
It is an additional object of this invention to provide an improved process for heating materials in an enclosure of which a wall portion channels the thermal radiation from a source region to a closure region, said closure region being susceptible to damage by said radiation.
It is a further object of this invention to provide an improved method for protecting a closure means of a thermal radiation carrying member from the radiation being carried by the material of said member.
It is an additional object of this invention to provide an improved method for heating semiconductor materials to high temperatures in an enclosure while maintaining a coupling or closure flange connected thereto at a lower temperature.
It is a further object of this invention to provide an improved method for cooling a coupling or closure means of a semiconductor materials processing enclosure.